Methods for forming elongated contact hole ends

ABSTRACT

Disclosed is a semiconductor processing approach wherein a wafer twist is employed to increase etch rate, at select locations, along a hole or space end arc. By doing so, a finished hole may more closely resemble the shape of the incoming hole end. In some embodiments, a method may include providing an elongated contact hole formed in a semiconductor device, and etching the elongated contact hole while rotating the semiconductor device, wherein the etching is performed by an ion beam delivered at a non-zero angle relative to a plane defined by the semiconductor device. The elongated contact hole may be defined by a set of sidewalls opposite one another, and a first end and a second end connected to the set of sidewalls, wherein etching the elongated contact hole causes the elongated contact hole to change from an oval shape to a rectangular shape.

RELATED APPLICATIONS

This Application claims priority to U.S. provisional patent application62/872,018, filed Jul. 9, 2019, entitled “Method for Forming ElongatedContact Hole Ends,” and incorporated by reference herein in itsentirety.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to formation ofsemiconductor structures. More particularly, embodiments of the presentdisclosure relate to methods for forming elongated contact hole endswithin semiconductor structures.

BACKGROUND OF THE DISCLOSURE

Fabrication of advanced three-dimensional (3-D) semiconductor structureswith complex surface topology and high packing density is populated withcomplex technical challenges. Some of these challenges are addressed formetal and dielectrics using directed reactive ion etching (DRIE).

During conventional one-dimensional (1D) patterning, such as contacthole elongation, via hole alignment, or space tip to tip push, the shapeof the hole or space end may be changed from a square or semi-circulararc to a sharper parabolic-like arc, as demonstrated in FIGS. 1 and 2.This change may result in a decrease in hole or space width at eitherend, which may result in a loss of contact efficacy. Maintenance of theshape at the end of the hole or space would therefore be desirable.

SUMMARY OF THE DISCLOSURE

In one approach, a method may include providing an elongated contacthole formed in a semiconductor device, and etching the elongated contacthole while rotating the semiconductor device, wherein the etching isperformed by an ion beam delivered at a non-zero angle relative to planedefined by the semiconductor device. The elongated contact hole may bedefined by a set of sidewalls opposite one another, and a first end anda second end connected to the set of sidewalls, wherein etching theelongated contact hole causes the elongated contact hole to change froman oval shape to a rectangular shape.

In another approach, a method of forming a contact hole in asemiconductor device may include providing the contact hole extendingthrough the semiconductor device. The contact hole may include a set ofsidewalls opposite one another, and a first end and a second endconnected to the set of sidewalls, wherein the contact hole has an ovalshape. The method may further include etching the contact hole whilerotating the semiconductor device about an axis of rotation extendingperpendicular to a plane defined by a top surface of the semiconductordevice, wherein the etching causes at least one end of the contact holeto change from the oval shape to a rectangular shape.

In yet another approach, a method of forming an elongated contact holein a semiconductor device may include providing the elongated contacthole extending through the semiconductor device, wherein the elongatedcontact hole includes a set of sidewalls opposite one another, a firstend and a second end connected to the set of sidewalls, wherein theelongated contact hole has an oval shape. The elongated contact hole mayfurther include a set of shoulder areas between the set of sidewalls andan apex of the first end or the second end. The method may furtherinclude etching the elongated contact hole while rotating thesemiconductor device about an axis of rotation extending perpendicularto a plane defined by a top surface of the semiconductor device, whereinthe etching is performed by an ion beam delivered at a non-zero anglerelative to the plane, and wherein the etching causes a material of thesemiconductor device at the set of shoulder areas to be etched fasterthan the material of the semiconductor device at the apex.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary approaches of thedisclosed embodiments so far devised for the practical application ofthe principles thereof, and wherein:

FIG. 1A depicts a prior art incoming hole pattern in a semiconductordevice;

FIG. 1B depicts a prior art incoming hole pattern in the semiconductordevice following various etch steps;

FIGS. 2A-2B depict a hole pattern in a semiconductor device followingvarious etch steps in accordance with embodiments of the presentdisclosure;

FIG. 3 is a graph demonstrating sputter yield versus ion beam angle ofincidence in accordance with embodiments of the present disclosure;

FIGS. 4A-4B demonstrate a change in angle of incidence and etch ratewith change in wafer/platen twist in accordance with embodiments of thepresent disclosure;

FIG. 4C is a side cross-sectional view of an angled ion implant to thesemiconductor device in accordance with embodiments of the presentdisclosure;

FIGS. 5A-5F demonstrate relative process times and wafer/platen twistangles in accordance with embodiments of the present disclosure;

FIGS. 6A-6B demonstrate an asymmetric etch achieved at a singlewafer/platen twist angle of 20° in accordance with embodiments of thepresent disclosure; and

FIG. 7 is a process flow for forming elongated contact holes in asemiconductor device in accordance with embodiments of the presentdisclosure.

The drawings are not necessarily to scale. The drawings are merelyrepresentations, not intended to portray specific parameters of thedisclosure. The drawings are intended to depict exemplary embodiments ofthe disclosure, and therefore are not to be considered as limiting inscope. In the drawings, like numbering represents like elements.

Furthermore, certain elements in some of the figures may be omitted, orillustrated not-to-scale, for illustrative clarity. The cross-sectionalviews may be in the form of “slices”, or “near-sighted” cross-sectionalviews, omitting certain background lines otherwise visible in a “true”cross-sectional view, for illustrative clarity. Furthermore, forclarity, some reference numbers may be omitted in certain drawings.

DETAILED DESCRIPTION

Methods and devices in accordance with the present disclosure will nowbe described more fully hereinafter with reference to the accompanyingdrawings, where embodiments of the methods are shown. The methods anddevices may be embodied in many different forms and are not to beconstrued as being limited to the embodiments set forth herein. Instead,these embodiments are provided so the disclosure will be thorough andcomplete, and will fully convey the scope of the system and method tothose skilled in the art.

Embodiments herein improve on conventional 1-D patterning holeelongation, such as the hole 105 shown in the devices 100 of FIGS.1A-1B, by enabling the shape of the ends of the hole 105 to be formedinto a desired shape. For example, by making the ends or apex of thehole 105 less pointed and more squared, contact area may be increased.Through the approaches described herein, custom hole end arcs and shapesmay be achieved.

FIGS. 2A-2B demonstrate a hole 205 or opening in a device 200, such as awafer, according to embodiments of the present disclosure. As will beappreciated, the hole 205 may be an elongated contact hole definedgenerally by a set of sidewalls 207, 208 opposite one another. In someembodiments, the sidewalls 207, 208 include one or more flattenedsections parallel to one another. In other embodiments, the sidewalls207, 208 are curvilinear shaped. It will be appreciated that thesidewalls 207, 208 may change from the curvilinear shape demonstrated inFIG. 2A to the parallel configuration demonstrated in FIG. 2B inresponse to an etch to a set of shoulder areas 214 of the hole 205.

As shown, the hole 205 may include a first end 210 opposite a second end212. In some embodiments, the first and second ends 210, 212 aregenerally symmetrical. In other embodiments, the first and second ends210, 212 may not be symmetrical. Each of the first and second ends 210,212 may be defined by the set of shoulder areas 214 joined at the apex218. As shown, the set of shoulder areas 214 connect respectivesidewalls 207, 208 to each apex 218.

It may be desirable to have a generally flatter apex 218 and square,wide shoulder areas 214. To accomplish this, the device 200 may berotated or twisted to increase an etch rate, at selected locations,along the first and second ends 210, 212. Wafer twist refers to rotationabout a rotation axis extending perpendicular a plane defined by a topsurface of the wafer 200 when the wafer 200 is clamped to the chuck andready to be processed. Twisting the wafer 200 with respect to the angledion beam changes the angle of incidence and the ion flux at every pointalong the curvilinear shaped sidewalls at the first and second ends 210,212 of the contact hole 205. As will be described in greater detailbelow, sidewall etch rate is a function of several factors includingangle of incidence and ion flux. In exemplary embodiments, the etch rateand therefore the shape of the first and second ends 210, 212 iscontrolled by wafer twist.

In some embodiments, different device twist positions are used during asingle wafer 1D patterning etch to “square off” the shoulder areas 214and/or the apex 218 so that the first and second ends 210, 212 moreclosely resembles the shape of the incoming or starting hole end, whichis depicted in FIG. 1A. For example, the etch rate at the shoulder areas214 may be greater than an etch rate at the apex 218. FIG. 2Bdemonstrates the contact hole 205 with squared first and second ends210, 212.

Etch rate is a function of several factors including the angle ofincidence between the incoming ions and the surface being etched. Forpattern wafer vertical surfaces of 3D structures, the angle ofincidence, Φ, is the compound angle resulting from the ion beam angle,θ, emitted from the ion source and the angle of the surface relative tothe scan axis, ω, such that:Φ=arcsin(sin θ sin ω)

On some platforms, θ can be controlled with ion energy, RF power and zgap, while w can be controlled with wafer/platen twist. FIG. 3 is agraph 300 showing the relation between ion angle of incidence andsputter yield, which correlates with RIE etch rate. Sputtering of atomsfrom a substrate is the result of the physical collision betweenenergetic ions, typically >100 eV, and atoms in the substrate lattice,which are dislocated and ejected as a result of the collisions. RIE alsodepends on ion collisions, causing lattice dislocations, to providereactive sites for the chemical reactions that drive reactive ionetching. Therefore, the RIE etch rate depends on angle of incidence Φ ina manner similar to sputtering shown in FIG. 3.

FIGS. 4A-4B show schematic top views, and FIG. 4C a side cross-sectionalview, of an elongated contact hole 405, including how angle of incidenceΦ and etch rate change with wafer/platen twist, proportional to w, forconstant ion beam angle, θ. For example, FIG. 4A may represent the wafer400 at a first twist location, while FIG. 4B may represent the wafer 400at a second twist location after rotating (ω) about an axis of rotation413. As shown, the angled ion beam 420 etches the material of the wafer400 at a non-zero angle relative to plane defined by a top surface 427of the wafer 400. The term “at a non-zero angle” unless otherwise noted,may also denote a single angle or a range of angles at least some ofsome of the angles being non-perpendicular to the plane of the topsurface 427 being impacted. Thus, when ions are provided to the wafer400 “at an angle” the ions may be provided over a range of anglesincluding positive and negative angles with respect to the axis ofrotation 413, and are effective to strike or impact the sidewall(s) 414defining the elongated contact hole 405, including at the first end 410and/or the second end 412.

Twisting the wafer 400 with respect to the angled ion beam 420 changesthe angle of incidence 1 and ion flux at every point along the sidewall414, which in turn changes etch rate of the sidewall 414. In exemplaryembodiments, the etch rate, and therefore the shape of the first andsecond ends 410 and 412, is controlled by rotation about the axis ofrotation 413, which may be optimized to cause the shoulder areas 444 ofthe first and/or second ends 410, 412 to be etched faster than the apex418.

More specifically, during operation, processing may include directingthe angled ion beam 420 into the sidewall 414 as part of an etchprocess. In other embodiments, the angled ion beam 420 may be directedat the sidewall 414 to form a treated layer there along. Processing maybe performed while the wafer 400 is in a first rotational position, forexample as shown in FIG. 4A. The angled ion beam 420 may impact aportion of the sidewall 414 between the top surface 427 and a bottomsurface 429 of the wafer 400. In some embodiments, the ion beam 420 doesnot impact the entire height or thickness (e.g., along the z-direction)of the sidewall 414.

The wafer 400 may then be rotated to a second rotational position whilethe ion beam 420 is processing the sidewall 414. Alternatively, the ionbeam 420 may stop prior to rotation of the wafer 400, and resume whenthe wafer 400 is brought to the second rotational position. As shown,the wafer 400 may rotate about the axis of rotation 413 by a rotationangle, ω. Although non-limiting, ω may be between 5-45°.

In the second rotational position shown in FIG. 4B, the ion beam 420 mayimpact a larger portion of the sidewall 414. As the wafer 400 continuesto rotate about the axis of rotation 413, the height of the ion beam 420increases until the ion beam 420 impacts approximately the entire heightof the sidewall 414, e.g., between top and bottom surfaces 427, 429. Insome embodiments, rotation of the wafer 400 and processing by the ionbeam 420 stops to prevent the ion beam 420 from significantly impactingthe top surface 427 of the wafer 400. In other embodiments, rotationcontinues, and thus the ion beam 420 continues onto the top surface 427for implanting or etching.

In some embodiments, as the substrate 400 is rotated between the firstand second rotational positions shown in FIGS. 4A-4B, respectively, thenon-zero angle θ of the ion beam 420 with respect to the axis ofrotation 413 remains fixed. More specifically, the ion beam 420 has thesame beam angle relative to the ion source while the wafer 400 rotatesbetween two different orientations. Furthermore, a voltage used togenerate and/or deliver the ion beam 420 may remain constant between thefirst and second rotational positions in some embodiments. In otherwords, the angled ion beam 420 and rotation of the wafer 400 provides auniform ion flux from top to bottom surfaces 427, 429 across the entirevertical height of the sidewall 414 without changing any ion sourcesettings and regardless of the device aspect ratio. This approachachieves continuous beam angle control. In other embodiments, thevoltage may vary between the first and second rotational positions.

FIGS. 5A-5E show the relative process times and wafer/platen 520 twistangles used to achieve the result in FIG. 2B, while FIGS. 6A-6B show theasymmetric etch result of various elongated contact holes 605 along awafer scan axis 635 using a single wafer/platen 620 twist angle of 20°.In this example, shoulder regions 644A and 644B are asymmetricalrelative to one another at a first end 610 of the elongated contact hole605 due to different etch rates. As shown, shoulder region 644A has agreater etch rate than shoulder region 644B. The second end 612 of theelongated contact hole 605 may also be asymmetrically etched. In otherembodiments, the first end 610 may be asymmetrically etched, while thesecond end 612 may be symmetrically etched. Embodiments herein are notlimited in this context.

Turning now to FIG. 7, a method 700 of forming a contact hole in asemiconductor device will be described. At block 701, the method 700 mayinclude providing the elongated contact hole extending through thesemiconductor device, wherein the elongated contact hole has an ovalshape, and wherein the elongated contact hole includes a set ofsidewalls opposite one another, a first end and a second end connectedto the set of sidewalls, a set of shoulder areas between the set ofsidewalls and an apex of the first end or the second end.

At block 703, the method 700 may include etching the elongated contacthole while rotating the semiconductor device about an axis of rotationextending perpendicular to a plane defined by a top surface of thesemiconductor device, wherein the etching is performed by an ion beamdelivered at a non-zero angle relative to the plane, and wherein theetching causes a material of the semiconductor device at the set ofshoulder areas to be etched faster than the material of thesemiconductor device at the apex.

In some embodiments, etching the set of shoulder areas causes the set ofsidewalls to extend parallel to one another. In some embodiments, anangle of incidence and an ion flux are optimized at the first and secondends of the contact hole to cause the set of shoulder areas to be etchedfaster than the apex. In some embodiments, the angle of incidence isdetermined based on the non-zero angle of the ion beam and an angle ofrotation of the semiconductor device about the axis of rotation. In someembodiments, the angle of incidence varies as the semiconductor deviceis rotated, while the non-zero angle of the ion beam remains constant.

In sum, embodiments herein provide a novel application over the priorart 1-D patterning hole elongation in which etch time is divided betweenelongating the hole or pushing the tip to tip bridge and forming orshaping the end of the hole or space. In a first advantage, embodimentsof the present disclosure provide asymmetric hole end arc formation tocustomize the shape of a hole, space, or line beyond that which may beachieved with EUV lithography and for a fraction of the time and cost.In a second advantage, embodiments of the present disclosure increasehole or space width at one or both ends of the elongated contact hole,thus resulting in an increase in contact efficacy.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” is understood as not excluding plural elementsor steps, unless such exclusion is explicitly recited. Furthermore,references to “one embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments also incorporating the recited features.

The use of “including,” “comprising,” or “having” and variations thereofherein is meant to encompass the items listed thereafter and equivalentsthereof as well as additional items. Accordingly, the terms “including,”“comprising,” or “having” and variations thereof are open-endedexpressions and can be used interchangeably herein.

The phrases “at least one”, “one or more”, and “and/or”, as used herein,are open-ended expressions and are both conjunctive and disjunctive inoperation. For example, expressions “at least one of A, B and C”, “atleast one of A, B, or C”, “one or more of A, B, and C”, “one or more ofA, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A andB together, A and C together, B and C together, or A, B and C together.

All directional references (e.g., proximal, distal, upper, lower,upward, downward, left, right, lateral, longitudinal, front, back, top,bottom, above, below, vertical, horizontal, radial, axial, clockwise,and counterclockwise) are just used for identification purposes to aidthe reader's understanding of the present disclosure. The directionalreferences do not create limitations, particularly as to the position,orientation, or use of the disclosure. Connection references (e.g.,attached, coupled, connected, and joined) are to be construed broadlyand may include intermediate members between a collection of elementsand relative movement between elements unless otherwise indicated. Assuch, connection references do not necessarily infer two elements aredirectly connected and in fixed relation to each other.

Furthermore, identification references (e.g., primary, secondary, first,second, third, fourth, etc.) are not intended to connote importance orpriority, and are used to distinguish one feature from another. Thedrawings are for purposes of illustration, and the dimensions,positions, order and relative sizes reflected in the drawings attachedhereto may vary.

Furthermore, the terms “substantial” or “approximately,” as well as theterms “approximate” or “approximately,” can be used interchangeably insome embodiments, and can be described using any relative measuresacceptable by one of ordinary skill in the art. For example, these termscan serve as a comparison to a reference parameter, to indicate adeviation capable of providing the intended function. Althoughnon-limiting, the deviation from the reference parameter can be, forexample, in an amount of less than 1%, less than 3%, less than 5%, lessthan 10%, less than 15%, less than 20%, and so on.

While certain embodiments of the disclosure have been described herein,the disclosure is not limited thereto, as the disclosure is as broad inscope as the art will allow and the specification may be read likewise.Therefore, the above description is not to be construed as limiting.Instead, the above description is merely as exemplifications ofparticular embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

What is claimed is:
 1. A method, comprising: providing an elongatedcontact hole formed in a semiconductor device; and etching the elongatedcontact hole while rotating the semiconductor device, wherein theetching is performed by an ion beam delivered at a non-zero anglerelative to a plane defined by the semiconductor device, and wherein theelongated contact hole is defined by: a set of sidewalls opposite oneanother; and a first end and a second end connected to the set ofsidewalls, wherein etching the elongated contact hole causes theelongated contact hole to change from an oval shape to a rectangularshape.
 2. The method of claim 1, further comprising etching a set ofshoulder areas between the set of sidewalls and an apex of the first endand the second end, wherein etching the set of shoulder areas causes theset of sidewalls to extend parallel to one another.
 3. The method ofclaim 2, wherein an angle of incidence and an ion flux are optimized atthe first and second ends of the contact hole to cause the set ofshoulder areas to be etched faster than the apex.
 4. The method of claim3, wherein the angle of incidence is determined based on the non-zeroangle of the ion beam and an angle of rotation of the semiconductordevice about an axis of rotation, wherein the axis of rotation extendsperpendicular to the plane defined by the semiconductor device.
 5. Themethod of claim 3, wherein the angle of incidence varies as thesemiconductor device is rotated.
 6. The method of claim 1, furtherwherein the non-zero angle of the ion beam is constant as thesemiconductor device is rotated.
 7. The method of claim 1, wherein theetching is performed at just the first end or the second end of theelongated contact hole.
 8. A method of forming a contact hole in asemiconductor device, comprising: providing the contact hole extendingthrough the semiconductor device, wherein the contact hole comprises: aset of sidewalls opposite one another; and a first end and a second endconnected to the set of sidewalls, wherein the contact hole has an ovalshape; and etching the contact hole using an ion beam delivered to thecontact hole at a non-zero angle relative to a plane defined by a topsurface of the semiconductor device, wherein the etching is performedwhile the semiconductor rotates about an axis of rotation extendingperpendicular to the plane, and wherein the etching causes at least oneend of the contact hole to change from the oval shape to a squaredshape.
 9. The method of claim 8, further comprising etching a set ofshoulder areas between the set of sidewalls and an apex of the first endand the second end, wherein etching the set of shoulder areas causes theset of sidewalls to extend parallel to one another.
 10. The method ofclaim 9, wherein an angle of incidence and an ion flux are optimized atthe first end and the second end of the contact hole to cause the set ofshoulder areas to be etched faster than the apex.
 11. The method ofclaim 10, wherein the angle of incidence is determined based on thenon-zero angle of the ion beam and an angle of rotation of thesemiconductor device about the axis of rotation.
 12. The method of claim10, wherein the angle of incidence changes as the semiconductor deviceis rotated.
 13. The method of claim 8, wherein the non-zero angle of theion beam is constant as the semiconductor device is rotated.
 14. Themethod of claim 8, wherein the etching is performed at just the firstend or the second end of the contact hole.
 15. A method of forming anelongated contact hole in a semiconductor device, comprising: providingthe elongated contact hole extending through the semiconductor device,wherein the elongated contact hole has an oval shape, and wherein theelongated contact hole comprises: a set of sidewalls opposite oneanother; a first end and a second end connected to the set of sidewalls;and a set of shoulder areas between the set of sidewalls and an apex ofthe first end or the second end; and etching the elongated contact holewhile rotating the semiconductor device about an axis of rotationextending perpendicular to a plane defined by a top surface of thesemiconductor device, wherein the etching is performed by an ion beamdelivered at a non-zero angle relative to the plane, and wherein theetching causes a material of the semiconductor device at the set ofshoulder areas to be etched faster than the material of thesemiconductor device at the apex.
 16. The method of claim 15, whereinetching the set of shoulder areas causes the set of sidewalls to extendparallel to one another.
 17. The method of claim 15, wherein an angle ofincidence and an ion flux are optimized at the first end and the secondend of the contact hole to cause the set of shoulder areas to be etchedfaster than the apex.
 18. The method of claim 17, wherein the angle ofincidence is determined based on the non-zero angle of the ion beam andan angle of rotation of the semiconductor device about the axis ofrotation.
 19. The method of claim 17, wherein the angle of incidencevaries as the semiconductor device is rotated.
 20. The method of claim15, wherein the non-zero angle of the ion beam is constant as thesemiconductor device is rotated.